JPS6036933B2 - Film stretching method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention heats a web of film in a tenter by an air duct/multiple heater combination placed in close proximity to the web, providing improved preferential heating in selected lanes; The present invention relates to a method and apparatus for stretching polymeric films that provide improved film properties.

Methods of selectively and preferentially heating polymeric films prior to stretching are known.

Tassler U.S. Patent No. 316171
No. 1 is an example of a known method in which a series of radiant heaters are suitably placed on the film directly above a stretching device, such as a tenter.

Such heaters are preferably spaced apart over the entire width of the film and parallel to each other in the direction of web movement. The heaters are individually controlled to preferentially heat the web while being substantially free of tension along at least one selective longitudinal lane. US Pat. No. 3,649,726 to Knowles shows a method for controlling the thickness of polymeric film structures.

In this case a heater of the type shown in Vietnam Pat. No. 3,161,711 is used to preferentially heat the web material before stretching. Simply put, in this method, the thickness of the film is measured at a certain position across the width before stretching, the thickness of the film is measured at a certain position across the width after stretching, and the thickness of the film is measured at a certain position across the width before and after stretching. Calculates the cumulative value of the film structure and determines the thickness of the film at any point across the width before stretching in response to deviations from a constant value in the film after stretching, which corresponds to the cumulative value of the film before and after stretching. This is a method of adjusting by letting the In this case, as in Yusler's patented heating method, the effectiveness of the heating depends on the effectiveness of the muta used. Other patents, such as Bay IJ-(Mother Ship Y)
In U.S. Pat. No. 2,339,451, other than a radiant heat source is shown for heating a web of film prior to stretching, in this case heating by multiple gas burners during lateral stretching. It is shown.

The burners are arranged in a zigzag pattern to prevent overheating of individual lanes. Additionally, U.S. Pat. No. 2,412,187 to Wiley et al. discloses a method for controlling heat input from an internally steam-heated radiator to separate portions of the web during machine and lateral stretching. and in US Pat. No. 3,304,205 to Ballard et al., it is shown to alternately heat the greens of the web in heated zones with a tenter to control the lateral stretch pattern.

The heating devices described here are radiant heat or air. A problem with this and other known methods is that they do not provide a way to effectively control the heating of the web in the tenter prior to stretching within very narrow limits.

The main reasons for this are the distance from the radiant heater to the web, or the inability to effectively separate the heated air impinging on the web. Many other attempts have been made to improve the thickness properties of extruded films.

For example, devices and methods have been developed for sensing thickness deviations and adjusting the thickness of a film at a particular point at or near the point of extrusion of a polymeric material during a film manufacturing operation. For example, US Pat. No. 3,122,782
No. 6, 2006, describes a mechanical arrangement for adjusting the thickness of selected virtual stripes across the structure of a film corresponding to thicker or thinner portions of the film.

In this patent, two interconnected multi-connect terminal plates are placed intermediate a gauge for sensing film thickness and an adjustment device for varying the width of the extrusion orifice from which the film structure exits and engages. A film thickness gauge measures the thickness of the film structure, which sends a tilt signal through the appropriate relay to the motor to drive it. The motor is constructed and arranged to open and close the orifice of the extruder in accordance with the deviation in film thickness sensed by the film thickness gage. US Patent No. 34
No. 55,175 describes an extrusion device with an adjustable lip including multiple adjustment screws along the orifice slot. This screw is about 2 pieces (
0.787 inch) and are interlocked into lips whose ends are modified by locally thinned cross-sections. Manual rotation of the 4 mm diameter screw moves the lip, thereby changing the entrance of the slot that defines the thickness of the web. Constraining the lip to a narrow area approximately equal to the width of a single adjustment is very difficult due to the inherent interaction of adjacent screws. Each change in screw setting inevitably results in a corresponding disturbance in the setting of neighboring screws, resulting in unpredictable deviation of the lip. To counteract this undesirable bias, the settings of nearby screws must also be corrected. The resulting narrow band or stripe non-uniformity is not easily removed without changing the basic gauge setting of the lip. Obviously, this type of regulating device requires constant human supervision and trial-and-error handling by experts. Conversely, the difficulties of relying on experts and trial and error are overcome to some extent by automatic gauge control systems, such as U.S. Pat. No. 3,122,784.

Its feature is that a number of controlled adjustment motors are mechanically coupled to a movable lip on the web extrusion device. The motors are located at a distance below the extrusion device and responsive to a signal generated by a lateral thickness sensing device that measures the final thickness of the web from a standard nominal deviation; an electrical signal is thus created and transmitted for effecting a thickness correction; by a switching device to the input of the motor. However, this pupil cannot eliminate narrow stripes or gauge band non-uniformities, since the individual adjustment devices only have a relatively wide section of the orifice slot. Further, the nature of the non-uniformity is often too subtle and complex to be properly adjusted by mechanical movement of die-shaped lips. A method is shown in U.S. Pat. No. 3,819,755, which provides an apparatus for selectively controlling the temperature (by heating or cooling) of discrete portions of a die lip of an extrusion die to improve thickness uniformity. It is shown.

Do not heat the web immediately before stretching. Finally, U.S. Pat. No. 3,341,388 discloses a method and apparatus for extruding thermoplastic films in which heaters are placed within the body of the die to heat these areas of the die to maintain a substantially constant sheet thickness. Are listed. Although these patents describe devices for controlling or related to the thickness of polymeric films, data suggest that preferential wafer lanes using heaters in air and thermally insulated areas have been proposed. It has not been shown to control the thickness of the film web in an improved way, as in the present invention, by actively controlling the heating of the film and preferentially heating only preselected areas of the film.

A problem arises when a lane adjacent to a lane selected to be heated is heated accidentally or for some other reason.

According to the present invention, this problem is solved by substantially preventing heat from escaping into adjacent pipes using the duct/heater arrangement of the present invention. Such controlled heating allows for a practical increase in temperature in a given lane, while minimizing temperature increases in adjacent lanes. In this way improved film properties are obtained. In summary, the method of the invention preferentially preheats the film before stretching in the tenter using heated air by means of an air duct located between and in close proximity to the interior green of the cup of the tenter carrying the film; The bottom wall of the duct has at least one aperture extending across the film, the aperture being spaced adjacently from the top surface of the film, preferably no more than 1 inch (2.54 cm) apart. The process consists of the steps of stretching the film in a tent.

More particularly, the method moves the unstretched web of film to operating conditions with respect to a heating device, which heating device moves the web of film from top to bottom of the duct. the duct has a number of intermediate walls between the side walls extending over its length in a direction, the duct further having means for defining at least one hole in the wall of the duct, the hole having a selectively heating the air passing through the duct with a heater positioned close to the surface of the film web and between the adjacent side and intermediate walls;
This involves preferentially heating the air passing through selected areas containing heaters without changing the velocity of the air through the ducts and holes, and then stretching the film.

In such a method, a tenter clip attached to an endless chain carried by a sprocket wheel grips the green web of polymeric film, placing substantially no tension on the film and moving it horizontally in a tenter frame. selectively heating the film along at least one selected longitudinal lane by directing heated air onto the surface of the web prior to stretching the film in such a direction; The web is heated by varying the temperature of an electric heater placed directly above the web, between the air guide walls at the web.

An apparatus for carrying out the method of the invention for stretching a web of film comprises a tenter comprising a number of tenter clips carried by two endless chains and guided by a track having parallel sections and unwidened sections; a heating device disposed between the clips of the top wall and proximate the surface of the web of film for selectively heating the moving web of film to a stretching temperature; a duct having a bottom wall and side walls, the duct further having a number of intermediate walls extending parallel to the side walls;
Each of the adjacent side and intermediate walls together with the top and bottom walls form a thermally isolated area in the duct, the duct further extending across the bottom wall and perpendicular to the side and intermediate walls. A heater is disposed between each adjacent wall having means for defining a number of holes and defining a thermally isolated area for varying the temperature of each heater, thereby increasing the temperature of a given heat. Means are provided for heating the air moving through the separated areas and preferentially heating the web with the air thus heated passing through the holes in the bottom. Preferably the heater extends from the top wall of the duct perpendicular to the top surface of the web at the entrance to the duct.

In other embodiments, the heater is electrically heated and extends the entire length of the duct. In a preferred embodiment, the bottom wall of the duct is no more than 2 inches (5.1 mm) from the top surface of the film web, and the side walls of the duct are 1/4 inch (0.64 inch) from the inside surface of the tenter clips. It's not too far away.

The heated air, which is substantially insulated in the duct area, exits the holes and impinges on the web of film, preferentially heating it in a new and useful manner as described below.

One key principle of the present invention is to insulate the heated air flow in the duct so that it hits only selective areas of the web.

Such air flow through the duct is selectively heated and exits the holes at a constant rate. However, there is a disadvantage, and therefore a problem, that must be overcome by the method and apparatus of the present invention. Because such walls act as heat sinks, the air adjacent to the side walls of the duct is cooler than the air in the central portion of the duct. By placing an air heating device or an electric heater between the intermediate walls of the duct,
controlling this separately and independently, thus increasing the temperature of the heated air between this intermediate wall, and of course controlling the temperature of the air near the side wall using a heater in the area defined by such side wall. I can do it. This means that the air leaving a selected area of the holes is heated to a higher temperature than the air in an adjacent area, and by insulating the heated air passing through the specific area and then through the holes and impinging it on a specific area of the wafer. This allows for control previously unknown in the art. Isolation of this heated air is also a key aspect of the invention. Without walls and selective heating devices,
Heat is dissipated to adjacent areas, lane resolution is reduced,
For example, unacceptably long response times may result. By thermally isolating the air to preselected areas, response times are more efficient and better controlled heat is obtained in a shorter amount of time. Thus, there is provided a method and apparatus for controlling film properties hitherto unavailable in the art. The present invention is a method for stretching polymeric films that includes the step and apparatus of selectively heating lanes of the film prior to stretching in a tenter. In its broadest sense, the present invention heats the film selectively in lanes by means of heated air directed toward the surface of the web, the air being heated by multiple heaters such that the temperature of the air in the selected lane is Controlled by selected heaters in the lanes, said heaters are placed between the air guide walls of the duct and consist of an improvement in which such air is directed to the web at its preselected location.

The method includes heating the polymeric film prior to stretching in the transverse direction. Next, the features of the method of the present invention will be explained in detail by considering the steps of the method with reference to the attached illustrations.

Referring to the accompanying drawings, a method of stretching a film web according to the invention is shown, which is carried out in an apparatus 10 according to the invention by means of a clip 12 of a tenter mounted on an endless chain 13 suspended over a sprocket wheel 14. , gripping the web of polymeric film F in a tenter 11 and, before stretching the film F laterally in the tenter, at least one selected one by directing heated air onto the surface S of the web. selectively heating the film F with substantially no tension along the longitudinal lanes, the air being heated directly above the wep between the air guide walls at such lanes. It consists of the process of heating by changing the temperature of the heater.

The apparatus for stretching the web of film F is constructed as follows.

The tenter 11 is attached to two endless chains and includes a number of tenter clips, 15 and 16 as shown.
It is guided by Suehiro's parallel track shown in .

A heating device 2 for preferentially heating the web of film F is placed between the clips 12 of the dentist in close proximity to the surface S of the web of film and heats the film passing therethrough to the elongation temperature.

This heating device includes a top wall 22, a bottom wall 23, a side wall 24,
25 and an inlet hole 26 and a closed end 27, the duct further has a number of intermediate walls 28 extending parallel to the side walls 24, 25, with adjacent side walls and intermediate walls each having an upper Z in the duct 21 with the walls and the bottom wall
-1, Z-2, Z-8 and Z-4 are defined.

The duct 21 further has means defining a number of holes 29 extending vertically across the bottom wall 23 of the duct and into the side walls 24, 25 and the intermediate wall 28.

Electric heaters 30 are located between each adjacent wall defining a thermally insulating area.

There is then a device 31 for varying the temperature of each heater 30, by means of which the air moving through a given thermally insulated area can be heated, the air heated in this way being directed to the bottom wall. 23 through which the web of film F can be preferentially heated. Preferably, the electric heater 30 extends perpendicularly to the upper surface of the web from the upper wall 22 of the duct at the entrance hole 26 of the duct.

In another preferred embodiment, the electric heater 30 is cylindrical and extends the length of the duct as best shown in FIGS. 2 and 8. In an important aspect of the invention, the bottom wall 24 of the duct is no more than 2 inches (5.1 c) from the top surface S of the web of film F; is located at a distance less than 1'2 inches (1.27 arcs) from the top surface of the web.

Additionally, the duct sidewalls 24 and 25 are no more than 1/4 inch (0.64 arc) away from the inner surface 12' of the tenter clip 12 in the preferred embodiment. The position of the duct with respect to the surface of the web to be heated and the inner surface of the clips of the tenter, in other words that the duct is placed close to the top surface of the web between the clips of the tenter, will be explained in more detail later in this book. This is the key to obtaining improved film properties with the invention.

Of course, it is known to use a tenter to stretch plastic films, fiber cloth, foils, etc. in the width direction.

A typical tenter generally includes a number of tenter clips attached to two endless chains and guided by a pair of wide divergent tracks. The clip is adapted to grip a web of material, such as polyethylene terephthalate film, as it emerges from a machine direction stretching device. Each track consists of two rails, an inner guide rail and an outer guide rail. The chain is moved around two or more motor drive members (usually sprockets) and is arranged so that it is guided in contact with the rails of the wide track as it moves. In this way, the chain clips move the web longitudinally and at the same time stretch the web laterally.
However, before stretching the film, it must be at or above a certain temperature, known as the stretching temperature. This temperature depends on the film's composition, structure, type, and stretching history (ie, whether the film has been stretched previously). For heating and preheating the film, tenters are usually equipped with heaters of the radiant or heated air type. During preheating, a low transverse tension is applied to the film to prevent it from tearing before reaching the thermoplastic state. Because of this process, the rails are substantially parallel. It is often desirable or necessary to heat the film to a greater or lesser extent in different longitudinal lanes of the film;
In particular, the film close to the tenter cup is heated unnecessarily. This acts as a heat sink, creating a temperature difference between adjacent parts of the film and the main part of the film, resulting in differences in thickness and properties. Among the sources of instability in selectively controlled radiant heat sources are the low absorption properties of the film (e.g. in polyolefins) caused by the low endothermic coefficient, such as in films filled with white or reflective particles. There is high heat absorption due to the high reflectivity and metal tenter clips that cause them to get too hot. In the case of air heating, the air is heated from a distant location and dampers regulate the heat by changing the air flow through separate ducts, so variations in flow create pressure differences that cause lanes and zones to change. Accurate control is difficult because of tension between the two. The method and apparatus of the present invention selectively adjusts thermal input to individual film lanes as the film enters the tenter before undergoing lateral stretching.

The main heat source is obtained by impinging heated air on the film. According to the invention, the heated air is further separated into a number of zones parallel to the direction of film movement, and an auxiliary adjustable electric heater is placed in each zone to vary the temperature of the air and The temperature of the web in the lanes can be varied to minimize gauge variations. As previously mentioned, it is known in the art to incubate a web prior to stretching in a tenter by means of a device that directs heated air through holes in a duct placed above the clips of the tenter.

As previously mentioned, this also means that the holes in the bottom wall of the duct are placed a considerable distance above the surface of the heated web (more than 2 inches (5.1 skins), approximately 8 to 12 inches (20.8 to 30 inches)).
．． The method of the present invention differs from the Ryoreki method in the above points. This also presents other problems and reduces the ability to control the heating of the web, at least within tightly defined limits. In known devices that use ducts to move heated air over the top of the web as the web moves between parallel tracks of the tenter, most problems arise due to the distance between the bottom of the duct and the top of the web. . However, tenter clips also absorb significant heat adjacent to the side walls of the duct, often resulting in inadequate or undesirable heating. The green part of the film is especially noticeable. This causes film loss, especially in green areas. The first aspect of the present invention is to place the air heating duct in close contact with the surface of the film carried by the tenter (
2 inches (5.1 inches or less) between tenters.

This allows the air exiting through the holes in the bottom wall of the duct to efficiently heat the web moving under the duct, significantly improving the properties of the film. However, a problem arises in that the air adjacent to and therefore in the vicinity of the side walls of the duct tends to be somewhat colder and therefore to produce uneven heating at the edges of the web.

There are also other problems known in the art, namely the unresolved problem with the location of the ducts between the tenter clips, often selectively heating certain lanes to improve the thickness properties of the stretched web. This is extremely desirable.
It is known to vary the properties of a stretched web, for example by varying the heating along the lanes of the web with constant thickness variations. The issue of positioning the duct between the clips of the tenter has not been resolved. The second essential step of the invention is to provide a device in the form of a heater placed between the intermediate walls of the duct in the insulated area of the duct, thereby increasing the flow velocity on the web and Selective web heating capability is provided by keeping the close distance constant.

With this principle in mind, the present invention will now be described in detail. Heating device 20 includes a number of individually adjustable elongated cylindrical heaters 30 placed on the upper surface of the web in the area of the duct adjacent to the web.

Each heater 30 or 30' is located in close, suitably spaced relation across the width of the film wap, and importantly, in Z-1 and Z-4 adjacent to the clips of the tenter. The edges of the web gripped by these clips are selectively heated during the heating process. A suitable heater of the elongated cylindrical type is described in Tassler, US Pat. No. 3,161,711. Heaters 30 and 30' (e.g. Calrod heaters) typically operate at a voltage of 50
It is operated at 50% of its capacity so that the temperature can be raised or lowered by raising or lowering it by around 50%.

In the preferred apparatus, the width of the heating device is adjusted by combining a suitable number of identical parallel longitudinal modules, and the film is moved as close to the tenter clips as possible. can be heated.

Each module has an individual internal heater and the whole group is connected to a voltage regulator (Variac).
c) Control panel with adjustable automatic transformer), ammeter and thermocouple indicators for the individual modules. These heaters 30 or 30' can extend through the length of the duct parallel to the direction of web passage, but are preferably of cylindrical shape and are located perpendicular to the upper surface of the wip and extend from the upper wall of the duct. It extends to a position close to the bottom wall of a given duct area (see FIG. 4). A device 31 is provided to adjust the voltage to these heaters, allowing their temperature to be varied as desired.

By selectively increasing the voltage to the electric heater in a given duct section, the air flowing through the duct past the heater in that section is heated to a higher temperature than the air in the next section. do. The intermediate wall 28 separates this hot air from the air flowing in adjacent areas, and such selectively heated air passes through the holes 29 to the upper surface of the wafer located adjacent to the duct; Selectively heat the web at this location. Although some heat is dissipated to adjacent areas, it is minimal and provides an effective method of selectively heating the web passing therethrough in a tenter. After heating, the film is transferred to a machine direction stretching device, such as spaced nip rolls, or a tenter frame as is known in the art and stretched. The film is then heat set in a generally known manner at various heat setting temperatures, after which it is wound onto a take-up roll for storage and use. Typical heating temperatures prior to stretching when practicing the present invention are shown in US Pat. No. 2,834,212.
Typical tenter devices are shown in US Pat. Nos. 3,118,212 and 3,727,273, and typical stretching methods are shown in US Pat. Nos. 2,823,421 and 2,995,77. By using the above-described apparatus in accordance with the above-described method, selected lanes, or groups of lanes, of the polymeric film can be selectively and carefully controlled to be heated just prior to applying a stretching force to the film. During the short time between heating and stretching, the thicker parts of the film cool down more slowly than the thinner parts, and the temperature difference between them becomes significant, so that when force is applied, the thicker parts deflect and are stretched, increasing the thickness of the film. Improve properties. A typical manufacturing process for films such as polyethylene terephthalate involves extruding the molten polymer through a die into a cooling drum, which cools the film and leaves it in a substantially amorphous condition.
Keep it.

The film is then passed through a first stretching device. This stretching can be done longitudinally by moving one set of silk at a higher speed than the other between two sets of rolls, or by using clips on a wide end tenter moving in a tenter. Transverse stretching can be achieved by stretching the film. Generally, one stretching method described above is typically followed by another to stretch the film in both directions, depending on the particular case. By monitoring the web thickness, appropriate heaters can be activated to heat the amorphous film or group of lanes after the film leaves the quench drum and before entering the lateral tenter stretcher. can.

To achieve heating of specific lanes, the invention uses a zone heater consisting of a number of electric heaters of cylindrical members placed longitudinally parallel to each other.

Such a heater is placed either directly above the slow nib roll or above the film directly above the film inlet depending on the subsequent stretching process. The distance between the heater and the slow nip roll or tenter is such that the unintentionally heated thin portion of the film is allowed to cool before stretching. There are many factors that determine this distance. For example, film travel speed, film thinness deviation, and heater temperature are best determined from the conditions of a particular experiment. Preferably, the heaters are placed across the width of the web of film and spaced one inch on center.

The temperature at which the film is heated is regulated by voltages connected to each heater.

This voltage is predetermined according to film thickness variations and travel speed. The extension rate of the thicker lanes can be effectively varied when the temperature difference with the thicker portion of the film is on the order of 0.1°C. Of course, the heater for the thickest lane will have a higher voltage than the remaining heaters. The voltages of the other heaters are adjusted according to the degree to which the corresponding lane is thicker than the desired film. The present invention is advantageous when used immediately prior to longitudinal or lateral stretching.
Any crystalline or crystallizable thermoplastic polymer can be used in making films by the method of the present invention.
Such polymers include polyolefins and their blends:
Polyethylene-2,6-naphthalene: Polytetramethylene-1,2-dioxybenzoate: Polyethylene-1
, 5 Naphthalate: Polyhexamethyleneazibamide:
Polyhexamethylene sebamide: Polycaprolactam:
and copolymers of ethylene terephthalate and ethylene isophthalate. Substantially amorphous, non-crystalline polymers can also be used, such as polystyrene.
A preferred method is to process substantially amorphous polystyrene terephthalate film. The invention is particularly suitable for making expanded polyethylene synthetic paper filled by the flat sheet process.

It is also suitable for transversely stretching other thermoplastic films, such as polyethylene terephthalate. The essence of the invention is to provide a method for selectively adjusting the heat input to individual longitudinal lanes of the film, rather than changing the overall heat input to the film. This allows the module duct heating bag to be used in the heating area of the tenter, placed between the tenter rails and very close to the top of the film, to control the temperature of the rails, and to control the temperature of the rails at right angles to the tenter clips. can be stretched across the entire sheet.

The invention is particularly suitable for preheating filled films. In summary, the present invention uses heated air by an air duct placed between and adjacent to the inner green of the tenter holding the film.
Prior to stretching in the tenter, the film is preferentially heated, such that the bottom wall of the duct has at least one hole extending transversely to the film, and then the film is stretched in the tenter. Contains processes.

In the duct, the intermediate wall defines heating zones of the duct, a heater is located in each zone, and the method further includes providing a voltage to the selected heater and passing it across the selected heater. To heat the moving air, this heated air is substantially separated from the air in other areas, moved through a duct, exits through a hole in the bottom wall, and passes under the hole in the selected area. preferentially heats the moving film,
The heated air exits the holes and impinges on the film web to preferentially heat it.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the apparatus of the present invention for stretching a web of film in a tenter, showing a heating device positioned above the film held in the clips of the tenter. FIG. 2 is a perspective view of a bag device that preferentially heats a web of film passing therethrough, the device being repositioned between greens inside the clips of a tenter carrying the web within the tenter. (not explicitly shown). 3 is a cross-sectional view of the device of FIG. 1 across the web, showing the heater located in a thermally insulated area of the duct parallel to the direction of travel of the web; FIG. 4 is a cross-sectional view of the device of FIG. 1 across the web; Figure 3 is a cross-sectional view showing a heater located at the entrance of the duct extending from the top wall of the duct. DESCRIPTION OF SYMBOLS 10... Film web stretching device, 11... Tenter, 12... Clip, 13... Endless chain, 14... Sprocket wheel, 1
5, 16...Truck, 20...Heating device, 21...
Duct, 22...Top wall, 23...Bottom wall, 24, 25
...Side wall, 26... Entrance hole, 28... Intermediate wall, 29.
...hole, 30,30'...heater, F...polymer film, S...web surface, Z-1, Z-2, Z-
3, Z-4...thermal insulation area. fiG. ZFIG. 1 f16.3 f16.4

Claims (1)

[Claims] 1. Prior to stretching in the tenter, the film is preferentially preheated using heated air by means of an air duct located between and in close proximity to the inner edges of the clips of the tenter carrying the film; The bottom wall of the tenter duct has at least one hole extending across the film, the hole being spaced no more than 2 inches (5.1 cm) from the top surface of the film, after which the tenter A method of stretching a film comprising stretching the film in a duct, the duct having an intermediate wall defining heated zones and a heater placed in each zone, supplying a voltage to selected heaters; heats the air moving across this selected area,
This heated air is substantially separated from air in other areas and is moved through ducts and out of holes in the bottom wall, thereby preferentially directing the film under the holes in selected areas. A method characterized by heating. 2. moving the web of unstretched film to operating conditions with respect to a heating device, the heating device having a duct, the duct having a top wall, a bottom wall, a side wall, and the progression of the film from the top to the bottom of the duct; the duct has a number of intermediate walls between side walls extending over its entire length, the duct further having means for defining at least one hole in the wall of the duct, the hole having a film selectively heating the air passing through the duct by means of a heater located in close proximity to the surface of the web and between the adjacent side and intermediate walls, thereby altering the velocity of the air through the duct and the holes; Claim 1: preferentially heating the air passing through the selected area containing the heater without first stretching the film.
The method described in section. 3 selectively heating the film in the lanes by heated air directed toward the surface of the web, the air being heated by an electric heater, controlling the temperature of the air in the selected lane by the electric heater in that lane, and heating the film selectively in the lanes; 2. A method as claimed in claim 1, in which the air is disposed between air guide walls, wherein such air is directed towards the web at its preselected location. 4 Grasping the edge of the web of polymeric film by a tenter clip attached to an endless chain carried by a sprocket wheel, applying substantially no tension to the film and stretching it laterally in the tenter frame. selectively heating the film along at least one selected longitudinal lane by directing heated air at the surface of the web, the air being heated at such lanes; 2. The method of claim 1, wherein the heating is performed by varying the temperature of an electric heater placed directly above the web between the guide walls. 5 between tenter clips containing a number of tenter clips carried by two endless chains and guided by a track having parallel and divergent portions and located close to the surface of the film web; a heating device for selectively heating a moving web of film to a stretching temperature, the heating device including a duct having a top wall, a bottom wall, and a side wall, the duct further extending parallel to the side wall. a plurality of intermediate walls extending in the duct, each of the adjacent side walls and intermediate walls forming a thermally isolated area in the duct with the top wall and the bottom wall;
The duct further has means for defining a plurality of holes extending across its bottom wall and perpendicularly to its side and middle walls, between each adjacent wall defining a thermally isolated area. The heaters are arranged and the temperature of each heater is varied, thereby heating the air moving within a given thermally isolated area, and the thus heated air passing through the holes in the bottom. 1. A device for stretching a film web, comprising means for preferentially heating the web. 6. The method of claim 5, wherein a heater extends from the top wall of the duct perpendicular to the top surface of the web at the entrance to the duct. 7. The device according to claim 1, wherein the heater is electrically heated and extends over the length of the duct. 8 The bottom wall of the duct is 2
6. The apparatus of claim 5, wherein the apparatus is spaced apart by less than an inch (5.1 cm). 9 The bottom wall of the duct is 1
6. The apparatus of claim 5, wherein the apparatus is located at a distance of less than /2 inch (1.27 cm). 10 The side wall of the duct is 1 from the inside of the tenter clip.
6. The apparatus of claim 5, wherein the apparatus is located at a distance of less than /2 inch (1.27 cm). 11 Heated air exits through the holes and impinges on the web of the film to preferentially heat it.
Apparatus described in section.